docs: def list(self, **kwargs):
          """
          Returns a list of :class:`MessagingStat` objects (messaging statistics).
  
          :Example:
  
          stats = client.stats_messaging.list()
  
          :param str by:    Group results by specified period: `off`, `day`, `month` or `year`. Default is `off`.
          :param str start: Start date in unix timestamp format. Default is 7 days ago.
          :param str end:   End date in unix timestamp format. Default is now.
          """
          response, instances = self.request("GET", self.uri, params=kwargs)
          return [self.load_instance(r) for r in instances]